text: Landauer stated that information is physical. His principle sets fundamental thermodynamical constraints for classical and quantum information processing. Much effort has been dedicated to incorporating information into thermodynamics and measuring the entropic and energetic costs of manipulating information. Gaining information, decreases entropy which has an energy cost. This energy has to be collected from the environment.  Landauer established equivalence of one bit of information with entropy which is represented by kT ln 2, where k is the Boltzmann constant and T is room temperature. This bound is called the Landauers limit. Erasing energy increases entropy instead. Toyabe et al. (2010) were able to demonstrate experimentally that information can be converted in free energy. It is a quite elegant experiment that consists of a microscopic particle on a spiral-staircase-like potential. The step has a height corresponding to kT, where k is the Boltzmann constant and T is the temperature. The particle jumps between steps due to random thermal motions. Since the downward jumps following the gradient are more frequent than the upward ones, the particle falls down the stairs, on average. But when an upward jump is observed, a block is placed behind the particle to prevent it from falling, just like in a ratchet. This way it should climb the stairs. Information is gained by measuring the particles location, which is equivalent to a gain in energy, i.e. a decrease in entropy. They used a generalized equation for the second law that contains a variable for information: 
  ΔF is the free energy between states, W is the work done on the system, k is the Boltzmann constant, T is temperature, and I is the mutual information content obtained by measurements. The brackets indicate that the energy is an average. They could convert the equivalent of one bit information to 0.28  of energy or, in other words, they could exploit more than a quarter of the information’s energy content.